From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758298AbcJZLZx (ORCPT ); Wed, 26 Oct 2016 07:25:53 -0400 Received: from merlin.infradead.org ([205.233.59.134]:36824 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753387AbcJZLZt (ORCPT ); Wed, 26 Oct 2016 07:25:49 -0400 Date: Wed, 26 Oct 2016 13:25:02 +0200 From: Peter Zijlstra To: Thomas Gleixner Cc: Tim Chen , rjw@rjwysocki.net, mingo@redhat.com, bp@suse.de, x86@kernel.org, linux-pm@vger.kernel.org, linux-kernel@vger.kernel.org, linux-acpi@vger.kernel.org, jolsa@redhat.com, Srinivas Pandruvada Subject: Re: [PATCH v6 5/9] x86/sysctl: Add sysctl for ITMT scheduling feature Message-ID: <20161026112502.GB3117@twins.programming.kicks-ass.net> References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.23.1 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Oct 26, 2016 at 12:49:36PM +0200, Thomas Gleixner wrote: > > + /* > > + * ITMT capability automatically enables ITMT > > + * scheduling for small systems (single node). > > + */ > > + if (topology_num_packages() == 1) > > + sysctl_sched_itmt_enabled = 1; > > I really hate this. This is policy and the kernel should not impose > policy. Why would I like to have this enforced on my single socket XEON > server? So this really wants to be enabled by default; otherwise nobody will use this, and it really does help single threaded workloads. There were reservations on the multi-socket case of ITMT, maybe it would help to spell those out in great detail here. That is, have the comment explain the policy instead of simply stating what the code does (which is always bad comment policy, you can read the code just fine).